Problem: If $x \star y = 2x-4y$ and $x \circledcirc y = 4x-7$, find $-2 \circledcirc (3 \star 0)$.
Answer: We don't need to find $3 \star 0$ because $x \circledcirc y$ depends only on the left operand. Find $-2 \circledcirc y$ $ -2 \circledcirc y = (4)(-2)-7$ $ \hphantom{-2 \circledcirc y} = -15$.